1. Field of the Invention
The field of the invention is that of digital mobile radio. To be more precise, the invention concerns the exchange of digital data by means of a mobile radio system to enable communications between two data terminal equipments (DTE), for example, at least one of which is mobile.
2. Description of the Prior Art
In known means of communication between two DTE using a wired line (such as the public switched telephone network) each DTE cooperates with an asynchronous modem, usually one conforming to the V.24 standard and to a modem protocol (such as the "Hayes" protocol (registered trademark), for example). These standards define an interface between a DTE and a data communication-terminating equipment (DCE) or modem.
Known digital mobile radio systems include the European GSM (Global System for Mobile communications) cellular system. Cellular mobile radio systems divide a geographical territory into small portions or cells each served by one or more base stations. This subdivision into cells enables optimum use of the radio frequency spectrum as more than one cell can use the same portion of the spectrum.
On the other hand, the cellular approach gives rise to various problems concerning call management, especially when a mobile changes cell ("handover"). There are further specific constraints in the case of the GSM system such as frequency redefinition, the use of frequency hopping, etc.
Another standard, the V.110 standard, has been drawn up for connecting a DTE to an integrated services digital network (ISDN). This standard has been adapted to the specific features of the GSM system. Accordingly, a DCE can communicate via the GSM system.
However, conventional portable DTE (microcomputers, etc.) are not equipped to communicate to the V.110 standard, but only via modems. It is not possible to connect such DTE to a cellular mobile radio network.
Also, the use of a cellular network is usually associated with the concept of mobility, and consequently with limitations as to the size of and connections between units. Consequently, the use of a dedicated adapter device is not an acceptable solution.
An object of the invention is to offer a solution to these problems. To be more precise, an object of the invention is to provide means enabling easy connecting of a conventional DTE to a cellular network.
Another object of the invention is to provide such means able to receive data signals and speech signals alternately.